A small-sized information processing apparatus, such as a portable telephone set or a mobile computer, is finding widespread application. Even these small-sized apparatus are mostly designed to display the image information. For example, certain types of the portable telephone sets of recent years are designed to display a variety of the image information acquired over the Internet.
The image displayed in small-sized apparatus is increasing in capacity in keeping up with the increasing processing speed of the image processing hardware or a variety of communication speeds. The apparatus having a display device of a large image format, such as a desktop computer, has a screen of a larger size and hence is able to display a high definition image at a time. However, in a small-sized information processing apparatus, such as a portable telephone set or a mobile computer, the display screen is mostly of a small-sized format, so that an image of a large capacity cannot be demonstrated at a time. Of course, the image can be demonstrated at the cost of resolution. However, in this case, the value of the information displayed is impaired.
Such a technique consisting in splitting a large-sized image into plural small-sized images and in sequentially switching these small-sized images for display on a display device with a small image format, and such a technique which consists in a display device unilaterally scrolls and demonstrates the image information as if one is winding and simultaneously reading a roll, have so far been used. The Japanese Laying-Open Patent Publication H-7-13554 has disclosed a technique similar to the latter technique.
However, with the former technique, in which gridiron-like small-sized areas, obtained on subdivision, are demonstrated sequentially one-by-one, so that these small-sized areas cannot be correlated with one another and hence the entire structure can hardly be comprehended. Moreover, if difficulties have been met in the division into the small-sized areas, the crucial information is split and displayed portion-wise on separate display sites, thus presenting problems that the structure of the entire image can in this meaning not be comprehended at a glance. In the latter case, in which the large-sized image is scrolled in the up-and-down direction or in the left-and-right direction, there is raised no problem of splitting the boundary location. However, since the image flows unidirectionally, it is difficult to recognize which position in the entire image is assumed by the currently displayed position. Thus, if it is attempted to re-display the same position, the position cannot be found without marked difficulties.
Thus, a wide variety of image information displaying apparatus, in which a frame by which a partial image of the entire image can be viewed in the entire image is set and this frame can be scrolled based on the observer's intention. For example, in the Japanese Laying-Open Patent Publication 2000-29568, a trackball is mounted on the back surface of a portable information equipment having a display and the portable information equipment is adapted for being moved on a table. As a result of this movement, the frame for demonstrating the image therein is shifted in the up-and-down direction or in the left-and-right directions. In the Japanese Laying-Open Patent Publication H-8-263205, a ball for detecting the direction and the magnitude of the movement is arranged on the back surface of the portable information terminal, so that a partial image responsive to movement on the table of this portable information terminal is demonstrated on a display arranged on the upper surface of this terminal. In the Japanese Laying-Open Patent Publication H-5-241731, there is disclosed an arrangement in which a movement sensor and a rotation sensor are arranged on the back surface of the main body unit to detect the magnitude or direction of movement or rotation.
In the Japanese Laying-Open Patent Publication H-8-314629, a ball for detecting the movement direction on the table is similarly mounted on the back surface of a flat-plate-shaped casing, having a built-in display, or the trackball is mounted on the upper surface of the casing. This allows scrolling an image in keeping with the movement of the casing on the table or with hand movement when the casing is fixed on the table. As for scrolling the image demonstrated on the display by acting on for example a direction key provided on the casing arranged on the table, there is a corresponding disclosure in the Japanese Laying-Open Patent Publication H-7-271506.
However, in an apparatus in which a casing having a built-in display is moved on a table or in which the casing itself is fixed on the table and a pointing device mounted on the casing is moved to display a desired image portion in the large-sized image, the following problems are met.    (1) For installing the apparatus, a planar surface, such as a desk or a table of a certain height suitable for operations, is required. The result is that it is practically impossible to scroll and display a portion of a large-sized image in case a portable telephone set or the like lightweight portable information terminal is being moved.    (2) Next, manipulation on a desk is comparable to pasting a large-sized map on the desk to observe its portion with a microscope. Consequently, the technique of arranging a ball on the back surface of the casing and moving it on the desk for moving an image demonstrated on the display is like the conventional technique of employing a paper sheet representing an image and hence appears to be more friendly to the user. Nevertheless, the problems similar to those hitherto encountered are raised. That is, if the image is to be observed on the display provided on the casing, which is moved on a desk, the image portion lying closer to the observer on the desk can be observed comfortably, however, the image portion remote from the user can hardly be observed on the display comfortably, because the casing is then moved to a location remote from the observer. The image can be observed comfortably from a direction perpendicular thereto, however, if the display surface is moved to the side of the desk remote from the observer, it may be an occurrence that the image is lost from sight or the portion of the transparent material on the image frame surface reflects light to render the image less visible, especially in the case of a liquid crystal display.
In the Japanese Laying-Open Patent Publication 2000-66802, there is disclosed a technique in which a virtual image frame is arranged on the desk at right angles to the desk surface and a liquid crystal display unit is arranged on a universal arm, with the display unit being then moved to different positions on the virtual image frame for displaying corresponding image portions. In this technique, there is raised a similar problem that, if the virtual image frame is increased in size, the image cannot be observed minutely, unless the observer moves his or her body upwards or towards left and right, depending on the location of the shifted liquid crystal display unit. Moreover, since the liquid crystal display unit needs to be mounted to the foremost part of the universal arm, not only is the apparatus increased in size, but also the large-sized image can be observed only on a desk portion where such special device is mounted, with the consequence that the site of possible application of the inventive concept is limited more severely than if the casing is moved on the desk.
It is therefore an object of the present invention to provide an image information displaying apparatus in which a large sized image can be observed in any location, using an image information displaying apparatus having only a small-sized display unit, such as the display unit of a portable telephone set or a mobile computer.